Using the --snaptime option

[Albert Peschar <albert@peschar.net>]

Hi all,

I've been using tarsnap for some months to do all kinds of backups.
Now, I'd like to use tarsnap to archive ZFS filesystem snapshots. What
is unclear to me is whether and how I should be using the --snaptime
option.

From the manual:

     --snaptime file
             (c mode only) This option MUST be specified when
             creating a backup from a filesystem snapshot, and
             file must have a modification time prior to when
             the filesystem snapshot was created.  (This is nec‐
             essary to prevent races between file modification
             and snapshot creation which could result in tarsnap
             failing to recognize that a file has been modi‐
             fied.)

Should I just specify any file that hasn't been modified during the
snapshot?

And would someone be willing to explain why this is at all necessary?


Thanks,

Albert